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|
// --------------------------------------------------------------------------
//
// File
// Name: NamedLock.cpp
// Purpose: A global named lock, implemented as a lock file in
// file system
// Created: 2003/08/28
//
// --------------------------------------------------------------------------
#include "Box.h"
#include <fcntl.h>
#include <errno.h>
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif
#ifdef HAVE_FLOCK
#include <sys/file.h>
#endif
#include "NamedLock.h"
#include "CommonException.h"
#include "MemLeakFindOn.h"
// --------------------------------------------------------------------------
//
// Function
// Name: NamedLock::NamedLock()
// Purpose: Constructor
// Created: 2003/08/28
//
// --------------------------------------------------------------------------
NamedLock::NamedLock()
: mFileDescriptor(-1)
{
}
// --------------------------------------------------------------------------
//
// Function
// Name: NamedLock::~NamedLock()
// Purpose: Destructor (automatically unlocks if locked)
// Created: 2003/08/28
//
// --------------------------------------------------------------------------
NamedLock::~NamedLock()
{
if(mFileDescriptor != -1)
{
ReleaseLock();
}
}
// --------------------------------------------------------------------------
//
// Function
// Name: NamedLock::TryAndGetLock(const char *, int)
// Purpose: Tries to get a lock on the name in the file system.
// IMPORTANT NOTE: If a file exists with this name, it
// will be deleted.
// Created: 2003/08/28
//
// --------------------------------------------------------------------------
bool NamedLock::TryAndGetLock(const std::string& rFilename, int mode)
{
// Check
if(mFileDescriptor != -1)
{
THROW_EXCEPTION(CommonException, NamedLockAlreadyLockingSomething)
}
mFileName = rFilename;
// See if the lock can be got
#if HAVE_DECL_O_EXLOCK
int fd = ::open(rFilename.c_str(),
O_WRONLY | O_NONBLOCK | O_CREAT | O_TRUNC | O_EXLOCK, mode);
if(fd != -1)
{
// Got a lock, lovely
mFileDescriptor = fd;
return true;
}
// Failed. Why?
if(errno != EWOULDBLOCK)
{
// Not the expected error
THROW_SYS_FILE_ERROR("Failed to open lockfile", rFilename,
CommonException, OSFileError);
}
return false;
#else
int flags = O_WRONLY | O_CREAT | O_TRUNC;
# if !HAVE_DECL_F_SETLK && !defined HAVE_FLOCK
// We have no other way to get a lock, so all we can do is fail if
// the file already exists, and take the risk of stale locks.
flags |= O_EXCL;
# endif
int fd = ::open(rFilename.c_str(), flags, mode);
if(fd == -1)
{
if(errno == EEXIST && (flags & O_EXCL))
{
// Lockfile already exists, and we tried to open it
// exclusively, which means we failed to lock it.
return false;
}
else
{
THROW_SYS_FILE_ERROR("Failed to open lockfile",
rFilename, CommonException, OSFileError);
}
}
#ifdef HAVE_FLOCK
if(::flock(fd, LOCK_EX | LOCK_NB) != 0)
{
::close(fd);
if(errno == EWOULDBLOCK)
{
return false;
}
else
{
THROW_SYS_FILE_ERROR("Failed to lock lockfile with flock()",
rFilename, CommonException, OSFileError);
}
}
#elif HAVE_DECL_F_SETLK
struct flock desc;
desc.l_type = F_WRLCK;
desc.l_whence = SEEK_SET;
desc.l_start = 0;
desc.l_len = 0;
if(::fcntl(fd, F_SETLK, &desc) != 0)
{
::close(fd);
if(errno == EAGAIN)
{
return false;
}
else
{
THROW_SYS_FILE_ERROR("Failed to lock lockfile with fcntl()",
rFilename, CommonException, OSFileError);
}
}
#endif
// Success
mFileDescriptor = fd;
return true;
#endif
}
// --------------------------------------------------------------------------
//
// Function
// Name: NamedLock::ReleaseLock()
// Purpose: Release the lock. Exceptions if the lock is not held
// Created: 2003/08/28
//
// --------------------------------------------------------------------------
void NamedLock::ReleaseLock()
{
// Got a lock?
if(mFileDescriptor == -1)
{
THROW_EXCEPTION(CommonException, NamedLockNotHeld)
}
// Close the file
if(::close(mFileDescriptor) != 0)
{
THROW_EMU_ERROR(
BOX_FILE_MESSAGE(mFileName, "Failed to close lockfile"),
CommonException, OSFileError);
}
// Delete the file
if(::unlink(mFileName.c_str()) != 0)
{
THROW_EMU_ERROR(
BOX_FILE_MESSAGE(mFileName,
"Failed to delete lockfile"),
CommonException, OSFileError);
}
// Mark as unlocked
mFileDescriptor = -1;
}
|
